Roland Juno-D distorting

hi folks. juno d…disassembled,replaced broken volume pot. sometimes after turn on works great. sometimes i get very distorted low output on both outs and phones on any patch. it never clears up unless i turn it off. for awhile. come back later, works fine again. i have read elsewhere of a bad ground causing this. any suggestions appreciated. some days i can turn it off and on throughout the day and the trouble never shows up.other times it happens at first turn on and doesn’t clear up til a day or so later. tried reboot. no luck. ruled out a bad jack or pot. stumped.